The popularity of green tea continues to grow along with findings that attest to its myriad of health benefits. Favoured by Chinese medicine for 4,000 years, research has now linked green tea to reduced risks of cancer and stroke, lower cholesterol, the prevention of cavities, natural weight management, and anti-inflammatory action as an aid for arthritis. These effects are due to the antioxidant capacity in the tea, the result of a high concentration of flavonoids, catechin in particular. Because green tea is made from fresh, unfermented tea leaves (unlike black tea which is fermented), oxidation of these catechins is minimal, allowing them to serve as potent antioxidants.
The catechins in green tea make up around 30% of the dry weight of the leaves. Of the catechins, EGCG is the most abundant and also shows the most anti-carcinogenic potential. Laboratory research has demonstrated the ability of catechins to induce apotosis (cell death) and inhibit the growth of numerous cancer cells. In addition, EGCG has been found to inhibit the enzyme urokinase that cancer cells may use to invade normal tissues.
Epidemiological evidence from green tea consuming countries such as Japan and China demonstrate low rates of cancer. Teachers of the tea ceremony (Sado) in Japan, a ritual way of preparing and drinking green tea strongly influenced by Zen Buddhism, are noted for their longevity and have particularly few deaths from cancer.
Human and animal studies suggest green tea may be preventive against a variety of cancers including bladder, colon, esophageal, breast, pancreas, rectum, and stomach.
In 1994 the Journal of the National Cancer Institute published an epidemiological study that indicated drinking green tea reduced the risk of esophageal cancer in Chinese men and women by nearly sixty percent.
Another study by a team of Italian researchers, reported at the 96th Annual Meeting of the American Association for Cancer Research, found that after a year’s oral administration of green tea catechins, only one man in a group of 32 at high risk for prostate cancer developed the disease, compared to nine out of 30 in controls. ‘Numerous earlier studies, including ours, have demonstrated that green tea catechins, or pure EGCG (a major component of GTCs), inhibited cancer cell growth in laboratory models,’ said researcher Bettuzzi, ‘We wanted to conduct a clinical trial to find out whether catechins could prevent cancer in men. The answer clearly is yes.’
The cholesterol-lowering effects of green tea and black tea have been confirmed by both epidemiological and animal studies. Green tea has been found to effectively lower ‘bad’ cholesterol and prevent its oxidation which may otherwise lead to plaque build up in artery walls.
The ‘French Paradox’, namely a high fat diet yet comparably low rates of heart disease, is believed to be due to the flavonoid resveratrol found in wine. In 1997, researchers from the University of Kansas found that the catachin EGCG is twice as powerful as resveratrol, which may explain why heart disease rates among Japanese men is quite low despite around 75 per cent of them being smokers.
In one 25 year study (the Zutphen Elderly Study; Hertog, M., et al., 1993), those that drank more than 8.5 ounces of tea per day had a much lower risk of experiencing or dying from heart attacks than those drinking less tea. Test tube studies have also found that green tea decreases the clumping of blood cells, reducing the risk of clotting associated with heart attacks and strokes (Sagesaka-Mitane et al., 1990).
Aid for Arthritis
The anti-inflammatory action of green tea, due to its flavonoid content, has shown promise for arthritis relief. Research by scientists at Case Western University suggest green tea antioxidants serve to postpone the onset and decrease the severity of one type of arthritis in mice (Haqqi et al., 1999)
Green tea has been espoused for oral health by asian practitioners and recent scientific research supports such. Studies in animals and humans have shown how green tea can effectively combat the bacteria that causes cavities in teeth. Green tea also contains fluoride that is protective for teeth.
Natural Weight Management
A study published in the December 1999 issue of the American Journal of Clinical Nutrition, indicates that substances in green tea extract may actually promote weight loss. Men given a combination of both caffeine and green tea extract burned more calories than those given caffeine or placebo alone.
The research, led by Dr. Dullo at the University of Geneva, examined the effects of green tea on ten young men for six weeks. In addition to a typical western diet (13 per cent protein, 40 per cent fat and 47 per cent carbohydrates), they consumed either green tea extract and caffeine, caffeine alone or a placebo.
The men’s energy expenditure (EE – the number of calories used in a 24 hour period) and respiration quotient (RQ – how well the body utilized carbohydrates, proteins and fats over a 24 hour period) was measured on 3 occasions during the study. Results found that the men taking green tea extract had a significant increase in their measured EE and significant decrease in RQ over those taking just caffeine or placebo. The men taking green tea extract also used more fat calories than the placebo group. There was no difference between caffeine users and placebo users in terms of fat calorie burning or overall calorie burning.
The scientists believed that the catechin flavonoids in the green tea extract may alter the body’s use of norepinephrine, a chemical transmitter in the nervous system, to increase the rate of calorie burning. They concluded, ‘Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.’
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